Effect of fish farming wastes on sedimentary and particulate organic matter origin in a Southern Mediterranean area (Gulf of Castellammare, Sicily): a multiple stable isotope study (delta13C and delta15N)

Carbon and nitrogen stable isotope analysis was used to investigate the dispersion area of waste material coming from fish farming activities in the western Mediterranean. Tests were conducted to see if uneaten feed and faecal material isotopic signals, originating from fish farms, could be detected in particulate organic matter (POM) and sedimentary organic matter (SOM). The detectable dispersion distance (from under cages as far as 1000 m) of cage-derived organic material was also examined. To do this, carbon (d13C) and nitrogen (d15N) composition in POM and SOM collected around the cages, in some control areas and in the waste material, was measured. Mean POM d13C was delta22.9F0.2x, while SOM d13C was 22.1F0.1x, and did not show significant differences along a distance gradient. Mean POM d15N was 3.9F1.0x, while SOM d15N was 3.4F1.3x, showing significant differences between 15N-enriched sites positioned near the cages and 15N-depleted sites positioned at about 1000 m from the cages. The mixing model applied to each reservoir (POM and SOM) as targets showed an incidence of autochthonous carbon (mostly phytoplankton in the particulate and sand microflora in the sediments) of about 24% in POM and of about 19% in SOM. Terrigenous carbon, which represented 37% in POM and 33% in SOM, increased in moving from sites nearby cages to more distant sites. Farming waste carbon represented 39% in POM and 48% in SOM. The inputs of autochthonous N represented about 24% in POM and about 18% in SOM, and with terrigenous N (representing 62% and 70%, respectively, in POM and SOM) showed higher contribution than cage-derived nitrogen. On average, farming waste nitrogen in POM was 15%, while it was 11% in SOM. d15NPOM showed a significant difference between cage sites and sites positioned at about 300 m. The latter was similar to sites located at 1000 m from the cages. Results indicate that in a Mediterranean oligotrophic area, with a bottom about 25 m deep and a mean current speed of 10–12 cm s 1, the influence of carbon and nitrogen from farming waste can be isotopically detected both in the particulate matter and the sediments in a wide area around fish farming cages. Sediments around the cages have been observed to be organic-enriched at about 1,000 m from cages. Dispersion of cage waste by hydrodynamic advection, consumption and defecation by wild fish, and resuspension from the bottom currents were invoked as three combined factors to explain the greater impact area found in this study than has been previously reported in the literature

Use of stable isotopes to investigate dispersal of waste from fish farm as a function of hydrodynamics.

Stable isotopes were used to examine differential effects of fish farm waste on the water column and sediments. To achieve this objective, we chose 3 marine fish farms located along the coast of Sicily (Mediterranean Sea) as point-source disturbances, and a control area. The hypothesis that carbon and nitrogen isotope composition of particulate (POM) and sedimentary (SOM) organic matter varied with increasing distance (from cages to 1000 m) was tested at 3 levels of hydrodynamics: low (mean velocity of current [MVC] ∼12 cm s -1), intermediate (MVC ∼22 cm s-1), and high (MVC ∼40 cm s-1). Different isotopic signals from allochthonous (fish waste) over natural (phytoplankton, terrigenous, and sand microflora) inputs allowed identification of the 'spatial effect regime' of fish farming. The increasing water current velocities seem to proportionally enlarge the relative area of influence of the cages, particularly on sediments. At low hydrodynamics, an increasing contribution of terrigenous signals was inferred: POM and SOM showing a depleted gradient of C (ranging from -22.0 to -24.0‰) and N (from 5.0 to 2.0‰). At an intermediate hydrodynamic level, C and N showed a slight increase in waste contribution, particularly in POM (δ15N from 2.6 to ∼4.0‰). At high hydrodynamics, an enriching isotopic gradient (δ15NPOM-SOM from 1.8 to 4.6‰) suggested a notable contribution of fish waste. Accordingly, the dispersal of waste from the cages seemed to be related to movements at the bottom of the water column, confirming the recently identified role played by resuspension movements

FEEDING-HABITS OF YOUNG-OF-THE-YEAR GREATER AMBERJACK SERIOLA DUMERILI (RISSO, 1810) ALONG THE N/W SICILIAN COAST

A survey was carried out from July to December 1992 in the Gulf of Castellammare (N/W Sicily) in order to study the feeding habits of juveniles of the greater amberjack Seriola dumerili. Stomach content analysis showed three different phases of predation during this period, depending on the size variation of the specimens. Cluster analysis suggested prey choice differed within three size groups. Class I (individuals up to 80 mm SL) feed mainly on the zooplankton community (Copepoda and Crustacea larvae). Class II (individuals ranging from 80 to 120 mm SL) represent a transition stage in which fish continue to feed on zooplankton, but benthic and nectonic items also become important. Class III (individuals greater than 120 SL mm) feed mainly on nectonic and nectobenthic items. Fish belonging to the size class II showed the highest value of niche breadth. The role of the Cymodocea nodosa system is stressed as an energy supply of invertebrate and vertebrate food items, especially to the size class II, in which fish shift from a planktivorous to a piscivorous diet. Further research is needed to understand better the feeding rhythm, food consumption and the role of benthic communities in the diet of this species

The effect of mariculture facilities on water column trophodynamics as revealed by biochemical features of suspended organic matter (South Tyrrhenian, MED).

A comparison of a Mediterranean aquaculture impacted area and control areas was made to assess the effect of fish farm waste discharge on the biochemical features of the water column. Trophic variables commonly used in marine ecology such as total suspended matter, suspended chlorophyll-a, biochemical features of particulate organic matter (proteins, lipids and carbohydrates) and biopolymeric carbon were chosen as the best descriptors of trophic conditions. An initial analysis of data from the impact area was carried out in order to test the effect of farm waste using a gradient of distances downstream from the fish farm cages (50 m, 300 m, 1000 m). The results were then compared with a control site 750 m upstream. Subsequently, the cage data set was asymmetrically compared with data from five controls collected some years before, when no aquaculture activity was present in the Gulf. The analysis revealed differences in chlorophyll-a, carbohydrates and some trophic ratios between the farm impact area and the controls taken upstream. A clear pattern of trophic enrichment of the water column around the fish farm was evidenced since concentrations in the sites increased along with their distance from the cages. The downstream sites overall were significantly different, trophically speaking, from the five control areas, while the trophic variables of the upstream control were not different from the external controls. Results showed that fish farm facilities provided an organic enrichment of the water column up to at least 1000 m downstream from the cages, producing a deviation of trophodynamics from normal ambient conditions

A Biochemical Genetic Study of Isoenzyme Polymorphism within and between Two Populations of Atherina Boyeri Risso

Allozymic variation of 20 loci was investigated in two samples of Atherina boyeri collected in the Mediterranean Sea from the coast of Trappeto and Marsala Lagoon (Sicily, Italy). Five loci were polymorphic (PGM*, EST-1,2*, SOD-2*, PGI-2*) and appeared to be in Hardy-Weinberg equilibrium. A significant Fst mean value (0.02) (G = 23.77, P < 0.05, df = 5) showed that the samples can be considered as two distinct local populations and supports previous morphometric discrimination